A spark plug in which a resistor is included for suppressing electric wave noise to be generated when spark occurs, has been known (Japanese Patent Application Laid-Open (kokai) No. 2013-187049). The spark plug disclosed in Japanese Patent Application Laid-Open (kokai) No. 2013-187049 includes: an insulator having an axial hole; a center electrode and a metal terminal which are disposed on the front side and the rear side, respectively, of the axial hole; and a resistor disposed between the metal terminal and the center electrode in the axial hole so as to be electrically connected to the metal terminal and the center electrode. Discharge current when spark occurs flows into the resistor.
However, in the above-described conventional technology, the current density of the discharge current is increased at and near the interface between the insulator and the resistor owing to the skin effect. Thus, if the amount of heat generation of the resistor at and near the interface due to Joule heat is excessively increased, the resistor is easily deteriorated from a portion thereof at and near the interface.
The present invention addresses the above-described problem. An advantage of the present invention is a spark plug in which the durability of a resistor can be improved by suppressing deterioration thereof.